Thread: Modifying a caravan to a flat bed

Currently looking for the right caravan to work on.

Figure by the time u purchased one it wouldnt be worth it. My suggestion is to price up the components to build from scratch, or buy a good secondhand tandem trailer.

I want it to be 2.3t GVM

For the kind of weight u are talking about, nothing short of a tandem van would be up to the task.

Would be concerned a really "cheap" van being a rust bucket chassis wise. Currently in the process of fixing up a couple of pop top vans when not working on customer units, so am gaining a real appreciation of the cost of second hand units.

Only my opinion.

Thanks Jatt

I am going to have a look at an approx 5m tandem van this Friday evening. IT is only 100 bucks so even if I just get springs and axles..... If necessary I will salvage what I can from it and start from scratch chassis wise but if its solid I will have a go at getting it banged into a flatter shape

I will be taking photos so feel free to comment on them as I go.

Shoudl have first update next week.

I've converted a couple of vans to trailers. I have always made ladder truss styled sides out of rhs and they really stiffen the van chassis.

The thing about a Caravan chassis (depending on manufacturer) is they're designed with the strength of the body structure in mind. Meaning that when you remove the body, the chassis loses alot of its structural integrity, without adding extra bracing and rails.

Good point boys. I will put some trusses down the side, looking at it tonight so pretty excited. Will post piccies if I can figure it out.

meh, did this last year. Had a derilict van, stripped it to the chassis, dropped a truck aluminium tray on it split fore and aft of the wheels, infilled with timber.

Mine's 4.6 long by 2.2 wide and registed for 750 kg just cos I could be bothered with weightbridge and roadworthy. I've had a meter of timber on it which is what ? 800 kg, and the thing itself weights 350 to 400. I'd happlity chuck 1.5 on it, but 2 would want some reenforcment.

Caravans are truely awful in their design. They start with a ridiculously heavy chassis, then build up a structure from as many bits as apossible to maximise leaks while minimising strength. In fact they are an object lesson in how not to build a structure of that sort. Then again people like me don't take jobs in the caravan industry

Ok so here is where it stands.

Chassis of the van is rubbish so i will be making a new chassis to take the axles and draw bar. Currently, it cetainly won't be up to the 3.5t GVM (yes I have revised and am going heavier than my oringinal post) that I want.

I have a main rail width of 1640mm to the outside of the rails. So I was wondering; What size 100x50 should I use for the main chassis rails and also the cross supports, would 2mm be enough or should I go heavier?

Consider this question with the fact I plan to use it as a timber carrying trailer of overall length of 6200mm not including draw bar. I may want to carry the occassional pointy log so sometimes it may need to deal with funky loads (hence it must be designed for that purpose.)

Next, I need to know what offset I need to place the tandem wheels behind the centre 3100mm point for correct balance on the tow ball?

Have you read this ?

http://www.infrastructure.gov.au/roa...pdf/vsb_01.pdf

regarding your question you want about 10% of the total weight on the ball, so imagine your trailer fully and evenly loaded, calculate the weight of the total and how far rearward of center you need to put the balance point. The space your 2 axles evenly front and rear of that.

Frankly, if your trying to design and build a trailer to carry that heavy a load and your asking where to put the wheels I can't help but wonder if you should consult and engineer, or just buy one. I think you'll need it certified to get past rego anyway, probably best to get the certifier involved early.

Cheers the PDF will help a lot.

I am building the trailer and just don't want to add more weight than necessary, hence the question on steel thickness. So has anybody got some hard facts on steel gauges to be used for a 3.5t vehicle, or would you all recommend not relying on this forum for information?