I have alway thought a diesel suburban would make a good expo truck. They stopped making them in 1999 but there are a few companies that will retro-fit a duramax in the newer ones. Spendy though.
From 92 until 95 or so they had the 6.5T with a non-computerized fuel pump. The later 90's had a more complicated fuel delivery system and there has been quite a few problems with it. There are easy fixes available though. The automatic transmission is fairly bulletproof if you don't do a lot of towing.
Driven at a reasonable speed it will get mid-twentys on the highway. Even with a good load. There is far more room in them than a 80 series. And a family of four will be crowded in an 80 if you are doing more that a weekend camping trip.
They are ifs front end so they ride fairly comfortably and they are big so you won't get them down quad trails. There are lots of upgrades available and every town in North America will sell parts for them.
They are not Toyota quality however. But with regular maintanence you should be able to keep it running nicely.
They are also quite rare, but easier to find than the diesel 60's and 80's in the states. They are LHD as well.