Not knowing what trailer you have--and even then, might not know its layout. But, locating the tank and uncovering all sides will be a lot of the battle. Most tanks are barely supported by angle iron along the long sides and may have a cross brace.
Why not get the tank completely clean and try some of the liquid fixes--JB Weld is one that should work if you get the right epoxy for the plastic.
Other than that, you will just have to learn as you go...
Wish you good luck.
And, welcome to the forum.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired