Attach U channel without dropping belly pan?

[thinktankair]

I have a section of floor I replaced which needs to be attached to the U channel. I have the inside skin off, but would really like to not drop the belly pan for many reasons. Is there a way to attach the U channel to the new plywood and frame without dropping the belly pan?

[RM66caravel]

Short answer not in my opinion but just my opinion. Save some time and frustration and do it right the first time. Drop the belly pan.
Cliff

[RickDavis]

Drill straight down through with a 1/4 inch drill, including the belly pan. Enlarge the hole in the belly pan to about 3/4 inch with a step drill.
Push a 1/4 inch carriage bolt up from the bottom and install a flat washer , lockwasher and nut . Lock tite doesn't hurt.
The belly pan holes are not noticeable and can be plugged with a hole plug or simply covered with a small piece of aluminum tape.
Dropping the pan on a 60's trailer is a major job.
I did all needed frame repairs, insulation repairs etc from above on my 61 before piecing in the new floor.

[Stefrobrts]

I was able to do mine without dropping the pan. Secured it with self tapping screws down into the frame, and smaller screws through the channel into the new wood. Has held up fine for ten years.

[thinktankair]

Thank you so much rick! What length bolt did you go with and what was the spacing? Every 5 inches or so? Rick, I so appreciate you saying it is a bear to drop the pan on the teailer. I thought the same and was doing well until this. Stef - did you secure the U channel into the wood into the wood only and that worked? I'm assuming your self tap went went down into the frame? BTW - my restoration blog is bambiairstream.com thanks all of you!

[RickDavis]

When the trailer was built the floor was secured with bolts with nut and then peened over so the would not unscrew.

Now days you can buy self threading floor bolts on Ebay or even in small quantities from tractor supply. They are a hardened , fine thread screw and seem to hold quite well.
some even pre drill although the ones I used required drilling a 7/64 hole and then power driving them.
I probably should mention the technique with the holes in my previous post was onlu used around the edges where the belly pan was to tight to reach in under the new pieces. The self threaders were used everywhere else the floor fastened

I used many more fasteners than Airstream did and their setup lasted 50 years

[Stefrobrts]

The channel was secured only to the wood, and the wood was secured to the frame. Just as Rick says, I used a high quality self tapping screw, and more of them than airstream used, and my trailer was 40 years old when I had to replace the front half of the floor. I think the repairs should hold up just as well.

[putback]

Worst case scenario and you need to get to the bottom side. You can pull it up on ramps unzip the belly pan seam, drill out the rivets on the flats and lower the sections enough to reach out to the edge from the bottom side. You may or may not have to cut and patch near the axle to get the pan sections low enough.