Boat ,Bike and box trailer all in one

It might be a bit more work, but how about you build a trailer frame and weld on some square section to take all the rollers or rails.
Then you could build a box to drop on the top after you remove the rollers with pins to go into a few of the roller holes. Then you can toss up wether it is easier to make a set of rails to hold the bikes in a similar slide on slide off fashion, or tie the bikes down in the box.

Hi BBB,
I have just joined up as a visitor so this will be my first response. You could build your 8x5 box trailer as normal, then what I have done with mine is to fit a removable frame to the inside of the box.Then to this I have fitted the bike runners,so therefore it is fully removable.You could also do this with boat rollers on a similar frame with wooden skids atached to the top of the sides.I hope this helps.
regards

Frosty01

www.belcocustomtrailers.com.au/landsea.htm

gmd

You only need to locate the front wheel of you bikes when in the trailer. I folded some sheet to a "u" section and bolted them onto the front inside wall of the trailer leaving a 50mm gap off the floor to allow easier cleaning. I made my own drop in assembly but found it a pain to store when not in use.

cheers

BBB,
ahhh - the ultimate all-round trailer search!
Considering your requirements, and that it's an 8x5 trailer, you have to make some compromises.
I have a similar issue when I sold my ute and upgraded to my Landcruiser T/D.
I had a 7x4 heavy duty box trailer custom-built by a Perth Trailer manufacturer.
My budget was $1600. I had an extra-long drawbar fitted so that I could put a lockable & dust-proof toolbox with 2xjerrycan brackets on it for my riding gear and tools, and/or fishing/camping gear.
Here is a good idea for when you want to transport multiple bikes. smart arse bike vice
I personally don't use one of these; I have never had the need to, and I have done a lot of driving with the bike(s) in the trailer.
A block of 4x2 wedged between the front guard and your front tyre will stabilise the front end - the rear tyre requires a ratchet strap/additional tie-down since it has a tendency to bounce around on corrugated/rough roads

Like other posters mentioned above and with the trailer's inherent restrictions, the removable cradle is your best option for the tinny; this will make launching it a bit stressful I think due to it's height off the ground.
In hindsight I think I should have ordered an offroad 8x5 trailer with a similar configuration (toolbox, etc).....but I recently bought a Trak Shak, and figured on getting one of these to be mounted to the back on the supplied reece-hitch
With a boat loader (to be yet fitted) and a folding bulldog trailer, I think I'll have all bases covered (it only carries one dirtbike though) ezimotow

Hope this helps.

Cheers,
Davo

There is this as well







From this mob, Trailer Made Campers

Baz.

BBB
Haven't seen or built one but here are my thoughts for what its worth.

Do you mean 5' wide (tray) with wheels/gaurds outside or underneath?

Box Trl: With removable front and back board. Hinges and Lock corners same as tabletop tray set ups.

Boat trl: Remove fr /bk boards, Drop in rollers to required positions as per normal along boat trl, set to height/spacings. Hand winch mounted on post, with U bolts onto trl frame or removable with same drop in fitting type as rollers.

Bike trl: Drop in bike wheel retainer, "C" shape as someone decribed, made as a frame for the 3 bikes (which could also hook/bolt to top of front board) and maybe using same system/holes as boat rollers and of course tie down points for bikes and boat.

Trailer floor height (for offroad clearance) may make boat launching/retreiving difficult, but a tilt set up built in would help if you want to go that way.

I can send photos of roller set up that I am picturing to better explain what I'm on about.