This is a topic I've read about previously and now that it comes time for me to install the running board covers I bought about 30 years ago from Steele on to my '37 LaSalle coupe I'm seeking advice.
I don't really want to use a 'one time stuck' contact cement.
I've also read pro and con on applying the rubber to a non-painted or painted running board.
Since it's well over $2,000 to get the boards covered today and the old rubber I bought is in perfect condition, I want to get it right the first time.
I'm leaning toward Loctite 5570. It comes in a caulking gun friendly so application will be straight-forward.
My running boards also have four depressions in each from the underside mounting bolts being over-tightened, and look impossible to tap out from the strut covered bottom side. I'm thinking of filling the depressions with bondo, so will have to test the adhesive to see if it sticks to metal, and bondo..or whatever filler I use.
The bolts on the bottom have round carriage heads that fit into a slot so just the nut shows, and mine were over-tightened causing the depressions. Each depression is about an inch wide x 4" long.
I do not have experience gluing down running board mats. I swallowed hard and had them recovered in Canada. I remember when Steele had mats we needed. They dropped those by the time I needed them.
I think any adhesive from a caulking gun might leave mounds through the mats where the lines of glue are. If not contact cement then think about something in a can that is spread with a notched trowel. That way the glue goes on in a uniform layer and makes for a flat mat surface.
Also I think it is necessary to spray a coat of paint over bare metal and bondo. Bare metal under the mats is an invitation for rust.
Just some thoughts.....take it or leave it.
There is a 'trick' to contact cement and that is to use wax paper.
Cover the (slightly warmed) adhesive applied area with wax paper and position your rubber in place with its adhesive applied.
slide the wax paper away and adhere perfectly, about 1" of the mat.
If it needs a redo ...It can be removed for another attempt.
Continue sliding Out the wax paper in managed amounts.
If they were sealed in a bag/container to be stored out of air and sunlight, then they might be OK, but can't tell how long they'll last once on the vehicle being 30 years old. There's antioxidants in there that get consumed over time, so they're no longer "new".
Pre-war is outside my interest, and what I recall, some of those were not attached by adhesives. A little research is needed before you glue. I'd talked to the guys that make/install them now. I used to see them advertise in Hemmings.
They use Loctite 55XX series black for rubber on the boats. I just replaced all the rubber, last year on my old boat after 14 years, it was weather cracked, with it. Whatever you decide to do, make sure you can reverse the process in the future when they'll need replaced again. I had to abraid the old adhesive off the fiberglass with a sponge sanding pad on the 2" right angle air grinder. So a painted surface will be damaged. That type adhesive is hard to work with and dries quickly(low pot time) and tough to remove, so plan out your job accordingly. You might get them out of position and not be able to adjust so some extra arms maybe wise or a slower curing adhesive. Dry fit before glue up. Make alignment marks.
The original rubber was most likely natural rubber and what Steele used was probably containing synthetics. Silicone rubber would last the best, but won't have the appearance of regular rubber. This is a common issue across all old vehicles, replacing factory rubber as it deteriorates quickly.
I glued the inner splash masticated rubber on with E6000 when the staples weren't available so gluing to steel is possible with correct adhesive and prep. 3M automotive has adhesives too. I'd stay away from regular "contact adhesive", the solvent may swell the rubber.
* If it was me, since something I could DIY, I'd take the boards off, do the metal work, repaint, then apply the rubber(off the car, if possible) Otherwise, all those imperfections will show when the rubber affixes. If a driver, probably not critical, but won't be on the lawn at Pebble.