Welcome to the Two Wheeled Texans community! 
Feel free to hang out and lurk as long as you like. However, we would like to encourage you to I know the original posting on this is from several years ago, but I wanted to share my recent experience with towing 2 bikes in a UHaul enclosed trailer. My friend and I needed to tow our cruiser bikes from Buffalo, NY to Sturgis last month for the annual rally. Initially, I checked into several different ways of getting our bikes there (other than riding them 1,500 miles one way!). We couldn't find anyone that had a trailer that we could borrow. We even posted want ads in Craigslist. I even considered shipping my bike to Sturgis, but it was too costly. My father had an open trailer we could use, but we both decided we wanted an enclosed trailer for such a large trip. It seemed the cheapest and easiest option was to rent a 6x12 UHaul enclosed trailer. So, that's what we did. We rented the UHaul trailer for approximately 10 days total, which came out to around $400 with taxes. We did not let them know we were towing bikes in this, as like others have said, I think they would not want you to do this.
I made several trips to the UHaul dealer and carefully measured the inside dimensions to make sure our bikes would even fit (We both have fairly large bikes: Honda VTX 1300R cruiser and a Yamaha 1300 cruiser). I initially thought we could bolt our wheel chocks directly to the floor as others here have suggested. However, after seeing the aluminum floor and how it was made, we realized there was no way we could do that without UHaul knowing about it afterwards. So, we purchased (2) wheel chocks at Harbor Freight. They work great and are a must in my opinion. After measuring the inside dimensions of the UHaul, we made a thin wooden floor out of 3/4" plywood. We also used 2x4's laid down on their side, on the outside to make a frame. This gave us room to mount the bolts to the plywood. We built the floor at my friends house ahead of time and made it in sections so that we could assemble it quick on the day we picked the UHaul up. This worked great. (See attached pictures) We installed (4) large tie down anchors for each bike - two for the front and two for the back on each bike. We staggered the bikes and they just barely fit. It is definitely a tight fit for 2 large bikes, but can be done. We then used (2) 2x4's on the sides and wedged them up against the roof so that the whole floor we made wouldn't hop off the trailer floor if we hit a bump. This setup worked great. We stopped several times on the way to Sturgis to check on the bikes, but neither one of our bikes ever moved at all inside the trailer. We probably spent around $200 to make the floor (including the wheel chocks & tie down points). We also purchased a fold-up aluminum ramp from Harbor Freight for another $125 or so.
Afterwards, we saved the wood floor in case we want to rent this same trailer again. We may consider selling it to someone if we end up not using it or maybe renting it to someone.
p.s. I purchased the canyon dancers, but found them to put way too much stress on the outside of the handlebars, so I do not recommend them.
I made several trips to the UHaul dealer and carefully measured the inside dimensions to make sure our bikes would even fit (We both have fairly large bikes: Honda VTX 1300R cruiser and a Yamaha 1300 cruiser). I initially thought we could bolt our wheel chocks directly to the floor as others here have suggested. However, after seeing the aluminum floor and how it was made, we realized there was no way we could do that without UHaul knowing about it afterwards. So, we purchased (2) wheel chocks at Harbor Freight. They work great and are a must in my opinion. After measuring the inside dimensions of the UHaul, we made a thin wooden floor out of 3/4" plywood. We also used 2x4's laid down on their side, on the outside to make a frame. This gave us room to mount the bolts to the plywood. We built the floor at my friends house ahead of time and made it in sections so that we could assemble it quick on the day we picked the UHaul up. This worked great. (See attached pictures) We installed (4) large tie down anchors for each bike - two for the front and two for the back on each bike. We staggered the bikes and they just barely fit. It is definitely a tight fit for 2 large bikes, but can be done. We then used (2) 2x4's on the sides and wedged them up against the roof so that the whole floor we made wouldn't hop off the trailer floor if we hit a bump. This setup worked great. We stopped several times on the way to Sturgis to check on the bikes, but neither one of our bikes ever moved at all inside the trailer. We probably spent around $200 to make the floor (including the wheel chocks & tie down points). We also purchased a fold-up aluminum ramp from Harbor Freight for another $125 or so.
Afterwards, we saved the wood floor in case we want to rent this same trailer again. We may consider selling it to someone if we end up not using it or maybe renting it to someone.
p.s. I purchased the canyon dancers, but found them to put way too much stress on the outside of the handlebars, so I do not recommend them.
