Jayco uses the BAL Ultraframe. Has no welding on it and uses a kind of rivet instead. This, plus the fact that Jayco has a decent reputation would make this my choice. Jayco was bought by Thor recently but I don't think Thor will change much. No big changes when they bought KZ a couple of years ago.
Forest River TTs seem to be hit and miss. I'd check the FR forum for specific info. on various brands/models. Don't know much about Grand Design but *think* they have a good reputation.
One important thing to look at first is frames. Check axle ratings (tag on axle) and tire load capacity rating vs. GVWR. Some (like Keystone) load these right up to their ratings. Look for at least 10 percent reserve capacity on tires. If a manufacturer offers the option, get higher load range tires. Look at CCC/NCC vs the GVWR. More CCC is better and can indicate strength of frame/suspension. Expect to add 500-1000 lbs of camping "stuff" including factory options plus upgrades/mods you do. Some TTs can have CCC as high as around 3K lbs and some under 1K lbs.
I'd also see what you can find out about factory support on issues and also how good/bad your dealer will be. Some are good, some are bad.
Since you're on the west coast, def. take a look at Outdoors RV (Northwood) TTs. They are better built than the majority of others and have many desirable features such as a heavy duty, off-road certified, in-house built frame c/w shocks and better insulation with 2" thick walls. Have a pretty good reputation. They're not part of a big conglomerate either.
