I put a spa on our dolly and had a team push it down the parade route. They promised never to do it again. Sorry, that was so long ago that I have FILM images of it, nothing digital.
The dolly I used was one of these -
We sat the spa down on it horizontally. We had some kids ready to ride in the tub, but we couldn't keep them sitting still and it rocked back and forth too much. They walked alongside handing out candy. We had two buckets of water and some dry ice to produce "steam." We ran out of dry ice before the end of the parade, but it wasn't working all that well anyway. To keep the water from slopping out I had 6 gallon buckets with only a gallon of water in each.
I have also set up a complete backyard scene on our flatbed trailer. We put down green outdoor carpet, a tub, a gazebo, some patio furniture and a barbecue. We had to really anchor the stools and have the people stand
next to them, not sit on them. I had a FogHog (smoke machine) in the barbecue. That worked great! I don't know if it was worth it - had to have a small generator just for the smoke machine - I had some music as well, but I could have just cranked the tunes in the truck if we had gone without the genny.
We took the roof of the gazebo off for the trip downtown and home again - I didn't want to watch in my rear view mirror as it came apart on the road. The rest of the gazebo did fine, even on the road.
Lots of color on the sides - bunting and such on the wheels. The usual stuff. We did the parade about three years and then gave it up.
Here is a site which can help you with the stuff you need to make your trailer look more like a float.
http://www.valleydecorating.com/howto.htmlWe bought a lot of stuff to hide the trailer, and none of it got used twice. So check this place out and see if you can get some better stuff to hopefully use again.
8-)