If you decide on plastic welding, make sure you use the same material as the bellypan. Take a piece of your welding material and weld the end somewhere on your bellypan. Let it cool and then try to pull it off. If it comes off easy it's not a match. Do this until the weld material actually sticks.
I took my dash to a local plastic welder here and rather than welding it for me he gave me a 5 hour lesson and I welded it myself. Anything can be used as welding material as long as it's the same type of plastic. We found a match with the different sheets of plastic he had in his shop and cut our own rods with his band saw. That way we could make a nice 1/2" wide welding rod. Try and create a V where the breaks are before you weld. Start by welding one end of the rod and push the rod towards the crack while aiming the plastic welder at the point where the rod and bellypan meet. Oh and make sure you don't melt right thru.
I tried welding before I went to see this guy and tried heating and dragging the rod. Oops.
I bought a plastic welder from ebay (same as harbor freight) and it stopped working a few hours after I tried using it. Luckily they're cheap.
I'm definitely not an expert but this is what I learned. It's an art.