Some excellent idea for you ljk from our experienced members.
I have used a powerful magnet to get me out of trouble on a number of occasions, and if what is jamming things up contains ferrous metal then it might be worth trying one.
A "Sea Searcher"magnet is the sort of power you need with a "pull" of around 140lbs (approx 64kg) its strong enough to act through the thin material of your locker lid or, as others have suggested, through the vent holes in the bottom of the locker ( you will need to remove the anti rodent grill from it and probably tape the magnet to a stick.
Be very careful when removing or replacing the "keep bar" from the magnet, the pull is sufficient to take off the top of a finger if you get it wrong! Use a handy brick wall as a lever.... ad don't forget to remove your watch to a safe place before removing the keep bar!
They are expensive to buy, around £30 or so, but most yachtsmen will have one somewhere and usually will be happy to lend it to you as long as you give it back when you have finished with it.
Here's a short video that will give you the idea:
https://www.youtube.com/watch?v=LFc8w1_kM4s
I have used a Sea Searcher for years and have recovered stuff (from anchors to tools to even outboard motors) so it may be worth trying on your caravan front locker.
Regards, and as always
Happy Caravanning
paws