You might already be aware, but there have been rumors that Trampier may have destroyed some of his manuscripts and art.  However, this has never been confirmed. Given that possibility, along with the apparent bad blood between him and some at TSR, as well as TSR’s periodic purging of materials, the chances of much of his art and manuscripts surviving seem bleak.

Here's an article I recently came across on him.

The Mysterious Disappearance of D&D's Greatest Artist - Knight's Digest

There are also some additional resources listed at the bottom of the article.

Sea-to-sky-games wrote in Trampier manuscripts?:Unrelated to TSR, which may be a footnote to some, Trampier was a designer of Titan, which is a game that continues to have lasting influence. It would be interesting to see if there's anything left from its decade-long development.

Ah, there's probably a lot better chance of that, since the late Jason McAllister, co-designer of Titan, did happen to keep some of the Titan products.

Stratochamp, possibly a couple of other Acaeum members, might have some of the design notes, early prototypes, or correspondence.

I have one of the first copies of Titan.  It was one of Jason McAllister's personal copies - the one he used at Titan Wars I.  It includes the Battlelands Expansion and a Titan Wars button.  It also has a letter of provenance from him.  Don't have anything else, though.