I don't own a FG trailer yet but I've made a front storage box for my current Coleman popup camper using a large marine Igloo cooler. I was looking for some sort of tongue storage box, and when I saw this big cooler at my local Costco, all I saw was my new storage box! The design matches perfectly the front of my camper.
I had to modify the hinges so the lid could be opened without interfering with the camper.
Also, setting up the camper would prevent access to the content due to the bed pulled over it, so I made some sort of 'quick-release' latches that allows me to remove the box from the tongue and put it on the ground just besides it when camping. I takes a second to put it back there, where it locks into place securely. This would not be necessary of course on a travel trailer.
My 20lb propane tank sits in there, securely attached. I had to relocate the gas regulators on the camper, and put a longer hose from the tank to the regulators. I cut a ventilation hole in the bottom on the box.
I use it to store levelling blocks, drain hose, etc.
The box does not interfere in any way with the tow vehicle, even in very sharp turns. It did interfere whit the tongue jack handle. I initially made a smaller one, but eventually I simply removed the handle and replaced it with a 5/8 coupler nut, and now I action the jack with my 18V deWalt drill and a 5/8 socket (which also works for corner stabilizers and cranking up the roof, so I'm done with the manual cranking on this camper!)
I have more pictures if interested.