We have an app in the works and in the meantime there is the standard mobile view of the site (no app to download). That mobile view should automatically load if you navigate tot he site on a small device.
Regarding search: The native forum search is....well... lame. It's a keyword search only. It returns all posts or threads that contain the words you are searching for. You can also search using the advanced search page for posts within a date range or by a specific member.
Here's a link to the advanced search page:
http://www.montanaowners.com/forums/search.php
I've also set up a custom Google search which will search this site using more complex search terms. You can try that here:
Montana Owners Forum Custom Search