I have an 87 34X and have towed it thousands of miles. I have been very happy with it.
Not to flame, but I feel they are built much better than Airstream. Their frame is superior in every way. Avion uses three 6" channels running the length of the coach, but they also have an 8" suspension frame that runs the length of the three axles plus a few feet off either side, so you have 14" of frame in the area of highest bending stress. You will never see sag or separation with an Avion.
It is true they are annodized. Avions were produced in the 1950's and 1989 was their last official model year, with some being sold in 1990. In the mid to late 70's, Fleetwood bought Avion (it was its own company prior to that) and they continued to have them built in the same plant in the same manner until 1989. At that point they quit making the silver Avions and slapped the name "Avion" onto large stick built fifth wheels (i.e. like Prowlers).
The basement models were only offered the last couple of years. There is nothing wrong with them, it's just that the company was on the decline when they brought them out and so they were some of the last models produced before Fleetwood pulled the plug on the aluminum trailers.
They were actually quite expensive: I have the sticker from mine and it cost over $33K in 1987.
As to weight, they are heavier than a similar year Airstream, but are lighter than the current Airstreams. They're not that heavy. For example, the gross weight on mine is 9600lbs and I know a later model 34' Airstream was quite a bit more than that.
The only downside I would see on your particular trailer are the rubber axles. I not like them; not Dexter, not Henschen, not Axis, not any of them. But, in 1988 Avion went to a similar type axle as Airstream used. They did it to cut costs. You would probably need to replace the axles because the old girl is 23 years old now and the rubber axles don't last forever. But you'd have the same issue on an Airstream.
My 87 uses what they called "Adjust-a-Ryde" suspension where they take a Dexter axle and cut it in half, then bolt it to a swing arm mount on the center of the trailer. Similar to Ford's "Twin I-Beam" front suspension. So what you get is six wheel fully independant suspension. There are six spring packs and six shock absorbers. It works wonderfully! I tow with 58psi in my Load Range D tires and I can set a plastic fork on the counter top and it's still there 500 miles later. I like this suspension better than the rubber axles because (A) it works great and (B) it doesn't wear out over time.
Google the Silver Avion Fellowship. Look up Dr. Donald Gradeless. There are silver avion forums as well. The guys on there get pretty hard core about them. Don says "...Airstream is built like a can, Avion is a Coach." Maybe a bit extreme, but they are built well.
They are an excellent rig. Very much like an Airstream but much more robust. The 34's tow like a dream too. I really love the triple axle. I towed mine 700 miles home, across the Great Smokey Mountains, with turns where I was almost looking at the back bumper, and then up the interstate at high speeds, just on the ball and it didn't sway at all. I now have a 1400lb capacity Equal-I-Zer and it locks her in tight as a drum.
I have no regrets about my Avion at all. Very happy with it! Yes, I wish I could mirror polish it. And, some guys have ground through the annodized layer and then polished them, but that is way too much work for me. Get some ParFe wax and rub her down and she'll shine right up beautifully.
About the price....if you looked on the Avion forums and found one in that condition, you'd be looking at more like $12-15K. I wouldn't dream of selling mine for less than $15K. But I have installed new everything in it. Like an Airstream, the shells last forever, but the appliances wear out over time.
Oh, look for ZipDee awnings too. They are much better than Carefree. I have five ZipDees on mine. You should too.
You will need a 3/4 ton vehicle for any trailer this size, but they pull great and don't listen to the baloney of "They don't turn" as that's not true. I heard all that mumbo jumbo before I bought mine and its hogwash. The triples tow better than any of them.
One last thought on edit....Cayo Mfg. built them originally and they are still in business. You can get many of the parts for them from Cayo to this day. They even work with Dexter to make new half shaft axles and stuff if you ever run over a Civic and bust an axle

Most of the other stuff is RV standard so it's easy to get stuff for them.
Hope this helps,