A seal test is a means of pressurizing the RV to test for leaks. You apply air to the inside of the RV by using the leaf blower usually through one of the roof vents. You then use soapy water along all joints, windows and seals to see if air is leaking via soap bubbles.
You might check YouTube for a video on how to perform one. A quick check of the forums here didn't produce anything but I remember reading how to do it before.
On a side note, did a factory tour of the Coachmen facilities this summer and at least on the TT line they did a seal test at the end of the line. Every unit got tested before it left the building.
Good luck, John