I've towed MGB's about 100 miles with a tow dolly and have always disconnected the drive shaft. Make sure the straps are on correctly especially the metal brackets that attach behind the wheel. I'd also strap the car to the dolly independently of the straps that come with the dolly, for added protection.
Make sure you bring spare wheels just in case and check all wheels before you go. I always bring tools to make sure nothing is frozen that I may need to partially dis-assembled.
I've only lost one and it's because of the metal brackets. I had them looped back to front instead of front to back and when the slacked a little, it lurched forward. Luckily it worked out ok but it wasted about 2 hours of my day, trying to figure out how to get it off the dolly and then back on again safely.
If I had my choice though, I'd rent the full trailer just for piece of mind.
If you take your time it should go fine.