Mount it from the outside using

ALLEN FULMER INSTALLING THROUGH-FIREWALL FILTER ON HIS RV-7

Mount it from the outside using 4 small nut plates on the inside. Cut a hole large enough to pass the body of the filter through, but not the flange.
After installation, test to see if you can pull the pin, turn and pull the filter apart. Be sure it has dual O-ring seals and reinstall. (Early filters have a single O-ring and should be replaced.)
Install a 90 degree 5/16 barbed x 1/4 NPT brass elbow, using LockTite 592 Teflon paste.
Install a section of fuel injection hose to your fuel pressure transducer, long enough that you can dislodge and clean the filter.