A 75 is awful tall so the length and width are not that great. Take a look at some other tank sizes, A 30 long or a 40 breeder would drop the weight without losing too much manuevering room.
A 40 breeder is 36" long by 18" wide by 16" deep.
A 30 long is 36" long by 12 5/8" wide by 16 3/4" deep.
Petco carries the 40 breeder tanks,
40But even with the lower weights, any water in them while traveling is likely to blow out the glue joints. You would have to empty the water when moving and transfer the turtle to something like a plastic storage container.
Also how big of a trailer are you looking at? there are several brands which make 25' and longer models with a pair of recliners or a sofa across the rear that would be easily set up to hold the tank instead. Which would keep it out of the slide.
Here is an example,
2520 passportOr for a larger one
2900 Passport