It seems that you are air-conditioning the space under the home. If it is cool under there the air is escaping under the home. You replaced the crossover so it appears that it is not where the problem is. You have good air flow on the back side of the home so you can assume that the problem is in the front side where your not getting sufficient flow.
You need to start just past the cross over and follow the duct work under the home. With a bit of luck you will be able to feel with your hand where the cold air is escaping. If not you will need to start exposing the duct work... By opening the belly board and inspecting the duct run, 'till you find the leak.
Once the problem is found and resolved be sure to repack the insulation into the floor and reseal the belly wrap. You should take precautions when opening the bottom and handling the insulation and use proper protective
Rolled fiberglass insulation has plenty of air space included in it. I like to use the highest R value, thickest, rolled, insulation I can fit into the space between the bottom of the floor joist and the floor decking, with our crushing it.
Once the insulation is in place you can purchase rolled vapor barrier material called Bottom Board by MH repair people and install it from below, stapling it to the bottom of the floor joist so it supports the insulation. You can find bottom board products at The Mobile Home Parts Store
For details about installing insulation and important safety tips see How to Install Fiberglass Insulation
and Crawl Space Insulation, from the U.S. Dept of Energy.