I made a slosher from plexiglass that I purchased at a home center.

The glue I used to assemble the slosher is plexiglass cement - it was hard to find, but eventually I found a glass shop that carried it. It's basically a solvent that softens the mating surfaces and allows them to adhere. To use it, it is essential that the cuts be precise since the mating surfaces must be in intimate contact.

Here's a dimensioned drawing (inches - I'm a dinosaur) for a slosher that holds 6 sheets and fits in an 11x14" tray