Entry level cost of building an Explorer Box(based on material cost June 2013)
An Explorer Box is built on a 4’ x 6’ frame. . There are a number of sources for 4’ x 8’ bolt-together frame kits which are easily shortened to be 4’ x 6’. Harbor Freight is a common source, their “Super Duty” frame kit on sale with 20% coupon has been $284 for at least a year now.. For a custom fully welded frame expect to pay around $1000. I also regularly see suitable used flat bed trailers for as little as $200 on craigslist.
You’ll need about $50 worth of clear grain pine 1×2’s for corner and shelf blocks. You have a few trade-offs to consider when choosing your plywood. If you go with ACX construction grade plywood, expect to pay $25 a sheet; you need four sheets. I normally use ACX construction grade for the floor, Baltic Birch ($45 a sheet) for the shelves / door backers and marine BS1088 Okoume ($109 a sheet) for the exterior. This combination saves 30-40 lbs and is very attractive with a clear finish.
This is another area with many choices. On one end of the spectrum you could go with House paint inside and out for around $40. I have not personally used it for a trailer box, but if you search the internet, you’ll find a number of small boat building sites promoting its use. If you think about it, your house is exposed to the elements day in and day out, the last time I painted mine was 10+ years ago and it still looks good.
For a durable colored exterior finish, I like a roll-on bed-liner material called Durabak. A gallon will do the exterior and run about $140. For clear exteriors and interiors I’ve been using Daly’s Seafin AquaSpar a water cleanup polyurethane, it runs $28 a quart.
This category has a few different things. First supplies like screws, glue, nuts and bolts and sandpaper will run around $35.
Then there is hardware. Basic hinges are $6, the cast ones I use are $13. There are many latch options, basic barrel slides are $3, the locking cam style I use are $15.
Door seals (two 10’ boxes) $16.
A tongue jack $35. If you plan to Tent Top your trailer a pair of rear stabilizer jacks should be added to the list, $38