Bob, I had my Morgan professionally under sealed with Dinitrol from new. The factory also uses Dinitrol now, less than a year ago when the local undersealer retired, Morgan brought the process in house, into a purpose build workshop.
Earlier this year I had my brand new MX5 professionally under sealed with Dinitrol.
When the professionals do it you need to leave the car with them for a few days.
They power wash the underneath, they remove the removable panels and inner wing covers, they leave the car in a heated booth to ensure the car. Is bone dry and they then mask up to protect the car from overspray.
Eddie Cairns on here, did a excellent video of the process on the MX5 forum.
