Thought I'd better provide an update for anyone interested in the outcome. Apologies for the lengthy post! First a quick shout out to Phil Tippler at Can-Am RV for his expert advice. He provided several email responses to my various questions relating to TV and AS selection, ideas on receiver modifications and finally on tongue weight weight reduction which was what initiated this post. Those guys are great and offer advice freely even to those that are not customers. True enthusiasts.
Anyway, a few photos attached plus a few comments / weights below. The tow home with the Cayenne Diesel was uneventful even for this novice wheel man. It pulls very well and was stable with no hint of sway (I'm using an Ea-z-lift and 2x husky sway control units). I did notice a very subtle porpoising motion occaisionally. The trailer was slightly nose down and a quick stop via a scale on the way home revealed the front axle weight was not quite restored which may have contributed some. I suspect some fine tuning of the setup would have improved an already good combination.
Some data on weights : -
Existing batteries were Interstate Class 24 and weighed 44 lbs each.
New batteries are 2 off 6V Lifeline AGM GPL-4CT batteries that weigh 62 lbs each.
I looked at 3 different possible positions for the batteries. Position 1 (where they are installed in the photo) is as far to the rear as possible - first picture, Position 2 just forward of the furnace under the bench and Position 3 under the fridge. Removal of the rear partition would be required to install here but there appears to be room.
The factory tongue weight was stated to me by Airstream as 844 lbs (catalogue for this model is 770 lbs but it does have the twin AC option plus a few other items so extra tongue weight was expected). I emailed the VIN to Airstream with a request for the as weighed data and they got back to me within a few days. They indicated this was the complete "as built" weight with batteries and full propane. Pretty good so far....
I weighed the AS tongue with a Sherline when I got it home and it weighed 900 lbs with everything installed as delivered (batteries, propane etc). A bit disappointed here. Not sure how the Airstream gained weight on the 50 mile tow home
I then set about taking items off and measuring the effect on tongue weight - weights at the ball cup were as follows: -
With factory batteries removed - 845 lbs
With new 6V batteries positioned (factory batteries removed)
6V batteries at position 1 - 770 lbs
6V batteries at Position 2 - 815 lbs (slightly rear of axle)
6V batteries at Position 3 - 845 lbs (batteries approx. on axle)
I'm planning on replacing the Airstream tires with LT's prior to my first long trip and deleting the spare so I then removed the spare to see what impact that would have. The spare was 48 lbs, the carrier remained but would remove maybe another 10 to 15 lbs. I will also be traveling with a full size TV spare (about 65 lbs) so I added 65 lbs of weight under the dinette to simulate this.
6V batteries in Position 1, AS spare removed and 65 lbs of weight under dinette - 710 lbs.
Based on the above I went ahead and removed the factory batteries and installed the new 6V batteries in the rear and also relocated the Inverter. I have not weighed the final configuration since the weather here has been uncooperative and the AS has snow on the roof. I also have not towed this configuration yet. I'm a little concerned over the large amount of weight to the rear of the axle and its impact on sway / sway recovery although % dry tongue with this configuration would be 11.6% which seems reasonable. if you are using a ProPride or Hensley sway dynamics with the extra weight in the rear is probably a mute point since these combinations can't sway in the first place.
You may be wondering what my goal is with this exercise, I'd like to get to 850 lbs tongue with a ProPride installed.
Next step is to hitch up, apply WD and go weigh on a scale to see what the actual tongue weight is with WD applied. The weather has prevented me from completing this last step so far - I want the roads clear of snow and dry before I tow so I don't get the AS covered in salt.
A few photos of the install included. Not quite complete yet, some tidy up to do but operational. I opted to run the cable inside under the bench, fridge and shower, along the wall, under the bedside cabinet and then into the front under bed storage area where the 12V
bus bars and inverter are installed from the factory. I used 2 runs of 2ga for the battery supply and return with a 100A marine breaker/disconnect on the battery positive line. For the Inverter hookup to the batteries, I used some of the wire used in the factory install and ran a 6ga ground and a phone line (remote switch) back to the under bed storage area to pick up the factory ground point and factory remote switch wire (the remote switch wire runs from the Inverter switch in the galley area to the under bed storage area). The 110A quick blow fuse for the inverter was also relocated to the rear and installed on the positive wire as close to the battery terminal as possible. The hitch jack wire needs to be extended from the battery box (it is connected directly to the battery) into the front storage area and then onto the positive bus bar. This requires carefully digging out some of the sealant where the cables pass through the floor of the front storage area to the outside. I took this opportunity to remove the battery and inverter cables that run from the battery box to the storage area and then resealed the hole.
I plan on covering the cables in the bedroom with a grey rubber trim piece that will be about 2" tall and 3/4" deep and stuck to the wall with double sided tape. It will look similar to the factory grey rubber trim piece that runs around the join between the floor and wall. Need things to warm up a bit before I do that. The only hard part of the install is tapping into the 110V inverter circuit. The inverter outlet local to the TV in the lounge area was "easiest" although getting a wire from the inverter to it is a PITA!
I'll report back when I have the actual tongue weight and some scale weights. I want to collect those before deciding to order a ProPride or not.