Scroll to the top of the page and look for the first blue box you see. Inside it is a search box with "powered by Google" in it. Click in that box and enter your search terms, then click the "Search" button to the right of the search box.
There are other ways to search spread around the page and within fora and threads. I recommend using the "Advanced Search" choice when you run across it.
You can also search directly from Google. Go to Google and enter a query like this one:
"Blue Ox" "towbar" site:irv2.com
This will give the same results as if you used the "powered by Google" search box with the "iRV2.com" button below the box selected.
Finally, here's a link
to the post from the forum administrators on how to search.