This is a pretty common concern.
We've had two toyhaulers, both models without a garage, and haven't had any problems with smell. We do take a few precautions:
<UL TYPE=SQUARE><LI>Primarily shutting off the fuel on the quads when they're in the trailer. <LI>We leave the roof vents open when traveling.<LI>Open everything up upon arrival.[/list]But this isn't usually necessary.
The hardest part is sleeping arrangements while still loaded. At best, we could sleep 5 without unloading, and that depends on what we're carrying. If you have to, just unload in the rain and tarp the toys, then you're good. It only takes a few minutes to unload, especially when motivated.
Don't forget that there are also models available with a separate garage. The limitation there is how many and what types of toys you're carrying. Most garages are 10-12' long and about 90-96" wide.