I'm suggesting (and only suggesting, mind) that the ply base with its timber or aluminium rails is probably quite stiff enough. (You did say that you could stand on it without it flexing much - so that's a 70kg+ point load. That's far more than you'd probably ever carry on the trailer, and if you did carry a heavy load, it would be distributed evenly over the trailer, not standing all in one spot).
Adding the bike frames seems unnecessary. So, yes, maybe try bolting the forks (without other bits of frame) into the wood frame.
You could try assembling the trailer both ways, with and without the bike frames. Then road-test it. Then you'll know whether retaining them is worthwhile.
Yes i felt that was what you were suggesting.
By the way i am 13 stone in weight, and 6ft 4" in height.That seems to be even more than 70kg, i'm still using lbs these days rather than kilos.
Your point is a valid one that i wouldn't expect to be carrying above 13 stones in weight.
I have spent so much time sanding these frames and headsets, trying to give them a clear silver natural finish that i am reluctant to give up on them, i weighed one of those bike frames last night and it was only 3lbs.The other one was 4lbs i think.
The plywood base by itself weighs 12 lbs.
and the extra chunky wood sidings weigh 2 lbs each.
The reason at first for using the cycle frames was to make sure the wheels were robust and wouldn't struggle with any terrain or object, at a variety of speeds, the fact that they also added strength to the underside of the trailer was a bonus, rather than the initial intention.
I was at first, last week, going to go the same route you are suggesting, until the idea of the frames came along.I was concerned that just a fork connected to a bit of wood was risky, even if strengthened with a section of aluminium and bolted on using u bolts.The frame idea then gave me much more confidence in the overall stability of the trailer.I thought to myself, there is no chance of this design falling apart.
But i admit, it is really over doing it.
"You could try assembling the trailer both ways, with and without the bike frames. Then road-test it. Then you'll know whether retaining them is worthwhile"
And yes i can try this suggestion of yours.
update:
I've uploaded a few more photos of slight changes made.
http://s270.photobucket.com/albums/jj86/port_soft/my trailer photos/
Both sections are cut now for the cycle frames to go through.And both forks are in line with each other, and the same height.I've shortened the bigger of the 2 forks by simply taking the spring out of the suspension.
I still have more sanding to do of the bike frames, this cheap tesco sander i had been using is fairly useless , and barely removed any paint, so i'm sanding by hand, removing all paintwork from the frames.After that i'll weather protect them.I also used a good name brand paint remover solvent, but it was struggling with the chunkier of the cycle frames, and was barely making a dent in the paintwork.
I think i will leave this thread for a week and see how far on i get, i don't need this trailer for immediate use, so am just taking my time, but the concept remains the same it will be as planned, a bed trailer.
To an outsider i think the cycle frames probably just look shabby and untidy, but i will cut these back more if need be, and may'be get them looking a bit less ugly.
Thank you to everyone who has contributed to this thread so far, you may inspire others with your ideas.Simply talking about it has shown the pitfalls, what to do, what not to do, where to start, what materials to buy.. etc.