There are a number of concerns based on your plans.
1. Each province as their own laws as to home base requirements but in BC specifically you need to have a physical address for your driver's licence and your medical. This can also be an issue when crossing the border into the US - they will ask you where you live.
Providing Proof of residency
You must be able to prove your residency if questioned. This is not only for the purpose of your driver’s licence or medical because you may be asked to prove where you live when crossing the border between Canada and the US so have receipts, etc with you just in case.
Your mailing address and your physical address do not need to be the same. It’s okay to receive your mail at a post office box or mailing service who will hold it for you or forward it to wherever you like. There is a fee for the service but it’s worth it rather than bothering a family member or friend.
You may be able to sneak under the radar for awhile and not actually have a home base but if something should happen and you need it in an emergency it wouldn’t be very good if your medical or driver’s licence was refused. It’s better to have a legal home base and keep everything legit. Each persons situation is different and therefore the answer to the question of having a home base may be totally different than other full-time RVers. Do what is best for you and what you are most comfortable with.
2. As to staying the in the US beyond the legal amount could lead to problems with income tax - you may have to pay tax in the US. And yes, as someone else mentioned you could lose your OAS and may not be eligible for medical benefits.
I have posted more information on my blog http://roamingrv.com if that helps.