I've been living fulltime in a toyhauler for almost four years. Mine is a 2006 Keystone Raptor 5th wheel, 38'. It actually measures out to a hair under 40'. It has a single slide-out in the living area and a separate 14' garage.
For fulltime living, it's fantastic. But as others have pointed out, it's not exactly economical to use for its intended purpose -- travel! Even with my diesel pickup, I get an average of 9 mpg.
Your plan for a smaller trailer is definitely a good one. But buying a new one may not be the best move. First, you should expect AT LEAST 25% off of MSRP. If a dealer won't do that, go someplace else. I got 35% off on this trailer ($42k out the door, no sales tax) because it was a two-year-old new leftover.
Look at used trailers. Look for bank repos. See what you can get those for compared to MSRP on the one you want minus 25-30% and see which is the better deal.
Get an extended warranty. Well worth it. The trailers themselves are decently made, especially K-Z's, it's the systems you have to worry about -- A/C, water heater, fridge, stove, microwave, furnace, etc, etc, etc.
BTW you didn't say what kind of truck you have (or if you did, I missed it)... I hope it's at least a 2500-series. I've never known a half-ton to do a decent job towing even a small toyhauler. A friend bought the smallest toyhauler he could find to tow behind his F150 SuperCrew. Three trips later and he traded the F150 on a used F250 SuperDuty Powerstroke because the F150 could barely maintain 55 mph on the freeway. Years ago, another friend bought a half-ton Chevy to tow his race car on an open trailer. Two years and four transmissions later (all under warranty), he got a 2500 with a Duramax.
So if you DO have a half-ton, please consider re-thinking your truck before you buy the trailer, or you'll end up doing it backwards and end up with a trailer that may be smaller than what you'd really want.
Rob