I've had bad experiences with drop in liners. They scratch up your bed if they don't fit perfectly and it'll be alot worse if you have sand under there. I'd say clean out the sand for sure and if you plan on hauling more sand, rock, etc., consider investing in a spray in bedliner. That's just my $.02

Good Luck!

 

on my 04 ram 1500 I pulled my dropin liner out a few months ago and without any sand under it was allready worn the paint wearever the liner touched it right down to the primer and its a factory liner so it fits nice and tight. so i have left it out and will be getting a spray on liner sence paint is worn on all the ridges in the bed now.

 

are there any downfalls to herculining the bed and then putting the drop in liner back on. it seems to me that it would offer the best protection since if you were to drop a brick on spray on liner you would still get a dent and that not the case with a drop in liner and vice versa.