I have not used the two-part (expensive) stuff, but have used insulating foam-in-a-can for lots of projects. I even landscaped the layout for my slot-car track with that stuff!
Tips and recommendations: Don't get in a hurry with this stuff.
Place the foam into the back corners of your cavity, and let it expand toward an exit port (probably the same hole you reached through to squirt in the foam). Otherwise you will end up with un-foamed voids that you cannot reach later. Fill only about 1/4 to 1/3 of the cavity with 'fresh' foam at first and let that much sit for a day or two (it don't take much!). The foam will expand significantly and that initial amount may end up being plenty. If not you can add a squirt later.
Leave vent holes. If you try to squirt this foam into a cavity and then seal it tight before it is cured, it can burst through a cardboard body tube or push a well-glued centering ring off the end of an assembly. I think these foams need open air circulation anyway to cure so you may not get a good result in a sealed compartment anyway. Plan for vent holes in a location that can be cleaned up afterwards.
Let the excess expanded foam spill out the vent holes but try to catch it on a sheet of paper or something so it doesn't fall back onto your work. If excess foam does somehow get onto the wrong places, LEAVE IT ALONE. It is easier to break off & clean off AFTER it has cured than to try to wipe it off while still gooey (boy, is that stuff sticky!).
Clean off cured excess foam with careful use of X-acto blades and with sandpaper.
Before using foam in contact with plastics check for chemical compatibility with scrap pieces. Your brand of foam may 'eat' some types of plastic, especially if the plastic is in the form of thin sheet material.
Plan ahead as to how you are going to seal the partly-used foam can (the stuff costs too much to buy a $4 can for only a two-second squirt) or else have a bunch of 'needs foam'-type projects lined up on your work bench ready to get squirted until the can runs empty.
Hey, solrules-
What part of SW Wisconsin? I still have family in Davenport, De Witt, and Madison, and drive from Dubuque to Madison about once a year. Are you anywhere close to the highway?