Did you use the stock plastic spacer? If you did, you can still use it, but you might find that a nice solid MDF spacer, with no gaps will improve midbass. I can't picture EK's too well, but if there are those little plastic pieces that fit into the door, that you screw into, remove them. They'll leave a 1mm air gap, coupled with a weak plastic spacer, that can rob you of midbass.

Use chip board screws to mount the MDF spacer, metal or tek screws don't have thick enough threads to really hold it in well.

A little clear silicone (NON acetic!) around the MDF spacer and door metal will keep it nice and sealed.

Acoustic foam works better for higher frequency ranges, Dynamat and other CLD's (constrained layer dampener) still work best for low frequencies near 100hz - Midbass. Even if you can twist a shops arm into selling you a sheet for roughly $30-25 or a wedge pack for $50 would be best.

Acoustic foam also absorbs water in a door, and might leave you with a wet dog smell in your car