Rick, welcome to iRV2.com. We are glad to have you join us here and we look forward to reading of your adventures and experiences.
You can cut off a small section at the bottom. You may find what is called a double bulb with sweep seal. It is a very common gasket used around slide outs and many rv repair shops usually have some in stock. There are different sizes and that is why you want a sample or you can have a shop order it for you.
It can be replaced by putting the slideout out half way and the seal is removed and a new on pushed and pressed back onto the extruded aluminum frame on the main wall.
Can you take a photo of a cross section and post it here?
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7