The artist states that he installs and tests most of his works prior to putting them up for sale. If you're that big of a fan, I would suggest emailing him to see if he would be open to you visiting to see any current projects he has installed. He might not want to do give you a full tour of his studio, but he might be OK with you swinging by to check out his "yard". He may also be able to give you a list of public installations for recent works.
The worst that can happen is he ignores you or says no to your requests, but asking certainly won't hurt anything.
Note that Mr. Howe lives on Washington's Orcas Island, so you will certainly be able to see the public works there even if you can't see the works in progress.