You can use a regular door. The standard ones off the shelf might not fit, all depends on the size.
Rather than trying to fit a standard size by adjusting the rough opening, you can just order a "Special". They are not much more expensive than a standard door. Just about any home center can do it. Typically takes a few weeks.
I had to replace my basement door. Really weird size like 78" x 50", just ordered a metal clad door via Lowes as a Special. Think it cost like $190. Had no choice as the foundation wall is hollow square masonary fired blocks. Could not change the rough opening with any degree of success. Probably got the best basement door in the county. Bit of a bear putting it in. Saved me that much in energy costs last winter.
Just remember to pull the casing and be sure to measure the rough opening correctly. Even if the door depth is a tad off, it is not that difficult to trim out. Same thing happens in old houses all the time. If you want a screen door just order a seperate one. Again they can be Specials if required. The quality of this approach will probably beat anything sold as a mobile door, most are junk to start life.
Also you must be able to describe the door exactly. The inner door is usually inswing, lefthanded, (hinges are on the right) or righthanded (hinges are on the left). Storm doors are usually outswing, again with whatever side the hinges should be on. Doors come in many different configurations standard but you can get it exactly as needed if ordered special. You need to get the description exact if ordering special. The factory has no way of knowing what you really need unless the order form tells them.
Like if you want a deadbolt or how many or exactly where. It will come predrilled. You might even be able to get the frame depth special or casing in a particular mode. Never tried to order one that way. If your trailer walls are only a 2 x 4 should still work. Some of them might have been 2 x 3.
One other issue that can come up in replacing mobile doors is how the siding is installed. If there is no casing (that lil trim board that runs around the door opening) and they brought the siding right up to the door jam, it can be a bear to get the old door / frame out. Can be done but you always are saying what where they thinking with this design.
If you have no experience with replacement doors, helps to have somebody that does or post some pics.