Tympan paper is the (usually yellow) paper on which you place your gauge pins to hold the paper for printing. Tympan paper is the top layer of your backing (usually redboard). You can adjust the depth of your (redboard) backing to ensure uniform printing pressure.
Boxcar bases allow the use of photopolymer plates, which come with their own adhesive. You must e-mail Boxcar a digital file of your design in Adobe Illustrator (vector) format AND send a faxed copy the same day.
The Boxcar base has a grid printed on top of it; you adhere your photopolymer plate to the base and then lock up the base with furniture just like regular typesetting.
The staff at Boxcar is extremely helpful and will guide you through the process. Tell them that you have a Kelsey 5×8 press and they will recommend the exact size Boxcar base for you. Be sure to ask them what size (depth) of relief you need to order for your photopolymer plates. That depth-relief number will never change for your plate orders, so put that number in your records. Their website has a wealth of helpful information, too.
Good luck!