Honestly, I have not sealed anything even though I bought some sealant, for this reason, and for the reason that I don't trust myself to give it an even coat. I just figure this stuff is so cheap to make I think of any one piece as disposable and easily replaceable.
The key is to move back further so the sealant is almost dry when it hits the foam. Alternatively, you could use sealers designed for foam - like the Army Painter version. Or do what I do - coat it in PVA glue thinned with water.
Although not required by a long stretch, I do like my foam cutter table and tools.