EDPM gaskets from Conservation Technology or others look like a durable way of air sealing but.  How are corners done with the gaskets? Are they mitered?  Is sealant used in the corners to "seal" the corner?   What other materials are suitable for use as building gaskets?  I'm considering using a strip of a closed cell foam made of a neoprene-edpm-sbr blend as a sill gasket-rim board air seal.

My belief is to keep it simple. the sill/rim is always spray foamed anyway, and we may start taping it as the new tapes stick to concrete, so caulking the corners of the EDPM gaskets is probably unnecessary. But may be helpful if you're shooting for <.1ACH@50p. The gasket has to be thick enough and compress well enough to seal the rough top of concrete which is never flat. That's why the rolls of pink or blue junk foam sill seal don't work and is the big advantage of the CT EDPM product.

I use a double 3/8" bead of F26 construction adhesive under the bottom plate. It air seals and adds strength to the structure. A big 29 oz tube costs $4.94 at the local Lowes. You get ~38' of 3/8" bead from a 29 oz tube.

Are you sure that works for you after, say, a year? I just took apart some assemblies today that I used construction adhesive on nearly a year ago. The adhesive part was working well, but it had dried up to a wisp and wasn't sealing anything. For the seal between the bottom plate and rough concrete, you might want something that won't shrink over time.  Like a sealant instead of an adhesive.

I doubt that the adhesive you mention was F26. F26 doesn't shrink any measurable amount. It is the same stuff that was used to bond my wood subfloor decking to my floor trusses to eliminate squeaks. Builders here use the stuff by the cases when building homes.

http://www.leechadhesives.com/F26products.htm

Adhesives work when there is no space to bridge between the substrates. Like between two pieces of dimensional lumber. Once you begin to have appreciable spaces, such as you get when one surface is uneven, you need to move towards a sealant.

A 3/8" bead of F26 will easily fill and seal a 1/4" void between the surfaces being bonded.  It has a pretty thick consistency and doesn't flow.  It looks similar to a bead of caulk when extruded from the tube.  Just much stronger.  Think of it as an adhesive sealant.

Think of it as an adhesive sealant.

Adhesive sealants are my favorite tube in the box to use. :-)