What you're talking about is a pretty common problem with fiberglass and non-FG trailers. We had problems like yours -- as well as many others -- when we bought our Surfside
. (See my Surfside
Refit Saga thread for details on that ongoing adventure.)
My first observation, assuming the door opened and closed easily before your trip and after you replaced the frame bots, is something has changed. Before you spend money on new hinges or anything else it makes sense to figure out what that thing is.
Yes, hinges are a candidate, but the more likely culprits are sag in the shell due to a deteriorating subfloor that isn't supporting the sides of your trailer, shell damage and sag, door damage and sag, problems with your new attachments between the frame and shell, or a warped frame. Figuring out where the problem is isn't too hard to do. All you need is patience, a bright flashlight and a 4' long level from a hardware store.
The first step is to park your trailer on a regular, level surface like a driveway and get your trailer set up and level, just s you would at a campsite. Now crawl under the front of your trailer with eye protection, reading glasses (if you need them), and your level. CAREFULLY inspect every point on the frame where there are bends for the tongue and every visible side where welds for cross-members occur. Do you see separations, deformations, lines of rust at joints or tears? When you hold your level up to the frame from below, are the parts that are supposed to be straight, straight?
If the answer to any of these questions is yes, you need to have your frame repaired by a welder who works on trailer frames or farm equipment. Make sure the frame-off the shell first: More than one FG camper trailer has gone up in flames when a welder skips this step.
Are the bolts you installed pulling the floor down snugly to the frame? Is the bottom of your resting uniformly on the frame? Does the frame and floor look level and straight?
If not, you may need to re-tighten your bolts or install painted wood shims to evenly support your trailer floor and you may need to take the trailer to a body shop and have it straightened. (Re-check for frame cracks/tears after straightening and once again after a couple thousand miles on the repair.)
Inspect the fiberglass at every part of the bends around the inner sides of the wheel well for tears. Tears suggest floor sagging and a need to both replace the floor and fx the sell.
Moving into the trailer, hold the level right-to-left across the floor at the front of the trailer and and at the door to see if the floor surface sags downward as it heads to either the street- or curb-side from the frame below. Also check for sag along diagonal lines, from the center of your trailer floor a few feet back into the front corners of your trailer. (Similar checks should also be doe in the back of your trailer, by the way. Wood rot can happen anywhere.) If you find sag over 1/8" (3+mm), your floor is likely rotted and the entire floor needs to be replaced. Double check the fiberglass around the wheel wells from the inside if you find sag.
If the floor of your trailer is rotted, you'll need to replace the rotted section all the way across, right-to-left, the width of your trailer, otherwise your repair won't support the walls of your trailer. A boat shop can do this repair.
Now inspect the sides of your trailer. Does the door-side bulge outward more than the street-side? If so, your roof isn't being supported properly and is sagging downward. This can happen when a floor rots or when non-fiberglass structural supports inside the trailer are removed, deform, or decay or because heavy hardware has been added to the roof (air condidtioner?) that isn't properly supported. Talk with someone who is familiar with fiberglass trailer repairs and modifications for next steps.
The core inside your door can rot, too. Now you know whether or not the shell has sagged or deformed, inspect your door to see if it is splaying out and away from the shell. if you A boat shop can repair your door if its interior has rotted.
Let's look at the hinges last. Are the screws tight? Do they screw into nuts on the inside of the trailer & door or do they screw into some hidden -- and possibly rotting -- wood that you can't see? When you remove the screws and hinges, do they come out too easily or are the screw threads rusty and filled with bits of wood? If so, the wood itself is rotting, and you'll need to install longer bolts, nuts, and washers to hold the door in place. Talk with a fiberglass trailer modder for ideas on how to best do this.