I recently purchased a home with a pier and beam foundation in northern Minnesota (climate zone 7A). The space beneath the house is enclosed by a wood stud skirting with a cement / stucco exterior. The bottom of the skirting is a wood stud resting on the ground. I’d like to encapsulate and insulate the crawlspace formed by the skirting, and I have a few questions I’m hoping you can help with.

1) Is there anything I can do to extend the lifespan of the wood studs used in the skirting material? Or should I just accept that it will need to be replaced eventually? 

2) Can I install rigid foam insulation directly over the studs on the interior? There is existing fiberglass batts in the stud bays. Should these be removed before installing the rigid foam insulation? 

3) What’s the best and simplest way to attach the rigid foam insulation to the studs? 

Thanks in advance for your assistance!