Denny in one word “NO”. They are called Dry transfers for a reason, they are not decals. You lay them on a dry surface and adhere them by rubbing them with a stylus or blunt pencil. They stick best to a rough surface, ie a flat paint. Just the opposite of water slide decals. No need to apply a gloss coat prior to lettering.
The transfers will come on a carrier sheet. Some are already laid out for proper spacing/alignment on the car side. Position the lettering so it is in the correct spot and tape one edge of the carrier sheet in place so it will not slip or move. Use the tape as a hinge so you can periodically check your work. Once positioned correctly (you only get one chance with Dry Transfers) take a stylus, blunt pencil, or similar and rub the carrier sheet over the transfer. Rubbing will generate heat which will fix the lettering to the car side. It does not require a lot of pressure, but you do want a uniform pressure over the entire transfer. You can tell when the lettering is adhered to the car side as the color will change under the carrier sheet and you can lift the sheet without lifting up the lettering. If some of the letter comes up, put the carrier sheet back down and run that area again (reason for the hinge).
Once all the lettering is place, then you can apply a flat finish to fix it in place.
If you have not used try transfers before I suggest you practice. Get a sheet of the Woodland Scenics alphabet lettering, and practice spelling out words on a piece of scrap. You will quickly learn how much pressure to apply (too much will tear the carrier sheet) and how to properly position and align the transfer prior to rubbing it.