The decision of whether or not to complete the repair yourself depends on a number of factors; time, money, interest, and expected results are a few.
If you are not interested in learning
fiberglass repair, or think you may never use and improve your new skills in the future, then I would recommend taking it to a boat yard (I am a retired boatbuilder).
I disagree with the comments here that you can simply look up instructions or watch videos and effect an acceptable repair.
Fiberglass repair is an art and there are many steps to it in achieving structurally sound and attractive repairs. This applies particularly to your 'stump' photograph. It takes years to develop the skills to make quality repairs.
Don't care that much about what it looks like, have time to burn, don't mind spending money on products and equipment you are unlikely to use again, short of money, just trying to get by? Do it yourself under those conditions and you will likely be satisfied with the results.
Glad you are attempting to address the problem and seeking advice on your options. I'm sure you will improve the trailer one way or another no matter what course you choose to follow.