oooo. A new turtle enthusiast. muahahaha.
I'm gathering from you question you will be adding support under the trailer for the tank? Is that correct? If so, then I'd say yes depending on how much and what kind of support you add. If/when you do have the added support put in, ask if the would rate it for a higher weight than that 75 as it sounds like you'll be getting a bigger one later. *
If you are not adding support then I couldn't tell you as I have very limited experience with what trailers can handle. If no one here can help, I'd ask a carpenter or other construction type worker who builds things.
Aside from a tank, I know people use rubbermaid tubs ment used as giant water bowls for horses. If you want kind of an indoor pond in your LR, they work nicely and are cheaper. Just a thought though.
PS- not sure if you know this but that tank will weigh about 750-100lbs once full depending on water level, gravel, etc.
*This statement/question assumes you will have someone else do the work.