practical stuff ... build-your-own links ... self-build plans
As well as the links below camper plans are frequently available on eBay. Try a search for 'camper plans' or 'truck camper plans'. You'll probably find some on ebay.co.uk but many more on ebay.com.
• ANGIB's site - Andrew Gibbens' site offers pdf and CAD downloads of plans for four different pop-up truck camper designs which, I believe, he has found elsewhere on the web. Sadly they include no contextual information and no details of materials or construction - they seem simply to be CAD drawing exercises. They may nonetheless be a useful starting point.
• Butler Projects - Paul Butler, US-based supplier of plans for boats and other items. The list includes plans for only one truck camper but it is a beauty in bent, varnished ply.
• Collapsible Truck Camper - more than just demountable, this camper is fully collapsible! Compact and basic, Unicyclerider64's camper can be put together in just 13 minutes as his YouTube video demonstrates. It appears, from the comments thread, that he is also happy to provide plans to those that require them.
• Glen-L - link to the recreational vehicle section of the Glen-L website. Glen-L sell plans for self-builders - of boats, motorhomes, 5th-wheels and travel trailers (caravans), as well as campers (demountables). The site has other useful links including photos of other builders' vehicles and a forum for exchanging ideas, asking questions and solving building problems.
• Good Plans Cheap - goodplanscheap.com is a curious website selling what appear to be one-off plans, drawings and diagrams which have been "carefully removed" from their original publications. The source publication of the plans on offer for a "stand-up pickup truck camper" is not identified but if you check out the link to 'Build a High-Low Pickup Camper' in the May 1966 edition of Popular Mechanics here, you'll notice a striking resemblance.
• How To Build Plans - howtobuildplans.com is another website, like GoodPlansCheap.com above, simply selling plans that are available elsewhere, in many cases for free. Their plans for a "Pop Up Truck Bed Camper" at $1.99, for example, are $1.99 more expensive than the identical plans available from Vintage Projects (see below).
• mobilerik.com - there's a lot of interesting stuff on Mobile Rik's blog/website which may have relevance and value to self-builders. In particular, although his camper is not actually a demountable, the plans of his own home-built project could well be useful. His eventual intention is obviously to sell the plans in book form but, for a limited time, you can download them (as a .pdf file) for free.
• Robert Q. Riley - another company selling plans to build just about anything, many of them drawn from Mechanix Illustrated and other old magazines. The list includes the 'Budget Camper', plans for a demountable which, at the time of publication, Mechanix Illustrated claimed could be built for $1200!
• Tumbleweed Tiny House Company - the tiny- or small-house 'movement', particularly strong in the States, can provide all sorts of useful ideas and inspiration but, as far as I know, Tumbleweed is the first company involved to deliberately extend into the truck camper market. If you fancy building a camper that's strong on charm and character, though perhaps a little less so on practicality, their 'Vardo' plans could be a great place to start.
• Vintage Projects - FREE plans for the real enthusiast! As their name suggests, Vintage Projects offer old self-build plans collected from a variety of sources including this classic pop-up demountable from the May 1967 issue of Popular Science magazine. The plans are immediately and freely available in .pdf format (You'll need a copy of Acrobat Reader on your computer to read them.) but are lacking in some detail so you may need to be creative. If you want to see the plans and accompanying article as they were originally published, you can do so on Google Books here.
• Vintage Teardrop Trailers - this teardropplans.blogspot offers exactly the same Popular Science pop-up truck camper plans as the Vintage Projects site (above) but for $9.99! I think that's what you'd call a no-brainer. Mind you, for that money you also get eleven other sets of trailer plans which you probably don't want and which are undoubtedly available for free elsewhere.
WHAT'S ON THIS PAGE
Links to websites offering to supply plans for home construction of a demountable pickup camper. Some are extensive and expensive, others are simple and cheap. One is even free!
As usual, if you find dud links here or if you feel there are major omissions, please let me know.