ol mate had a 7x5 with a 3 piece front wheel bracket that slotted into some holes so he could easily convert from general trailer to bike trailer in 2 mins
That's the go, saves the nut and bolt gig.
Ken, this is what a young bloke down the road has. His needs are as yours.
I have seen him rip the dump and furniture cage sections off in a few seconds with a rubber hammer too.
One of things I will never have again is a NON-GALVANISED box trailer.
The rot sets into painted box trailers very quickly, no matter what. The one above is only a couple of years old and well on its way.
8 x 5 trailers aren't much dearer given that sheet stock sises comes in 8 x 4 to start with.
Make sure its draw bar is an A frame long enough to fit one of those large aluminum boxes to.
In NSW if the empty unladen tare weight is under 250kg then your yearly rego fee is only $60, but the moment it goes over 250kg it jumps to $160, even if it is still a 750kg gross with-out brakes.
So now a combination of Galvanized Aluminum trailer under 250 tare will pan out to be a great investment and they are not very dear either and plenty of local manufactures to choose from these days.
Maybe a couple of jerry-can holders to, one for water and one for fuel.
http://www.ebay.com.au/sch/i.html?_odkw=&_osacat=66468&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xaluminim+box+trailer.TRS0&_nkw=aluminim+box+trailer&ghostText=&_sacat=66468