actually it isnt that heavy, well unless you compare it to paint. yes you can use bedliner in the trunk, in fact there have been people use it instead of paint on the whole vehicle! usually on offroad vehicles.
what i done is went to advance and get some undercoating and sprayed the entire trunk area. then sprayed that splatter paint stuff in the areas thats seen and put the factory style mat down. dont look bad at all
I used brush on bed liner for all of my undercoating after stripping down the entire underneath. It looks much better and seems to be very tough. No problems yet. The brush on stuff even smooths out well, not showing the brush marks.