Here's a link for a product that links three EU2000 Honda generators:
http://www.wisesales.com/triple-parallel-kit.html
I have seen a better connector box but it will take me a little why to locate a link. I am not endorsing nor recommending this product. I recall from my electronics days that some synchronization is required and I don't know if these cables do this correctly and I am not willing to try this with my own equipment until I know all the answers. But this gives you the idea of the possibilities. Unfortunately I don't know how well this works or how practical it would be, but it sure seems to suit the small portability of some very clean power.
ON EDIT: There is no other solution that I can find. I thought I saw one where the 50 amp box had a gauge. This is a newer version and has no gauge. I was able to see that on the link it is the same provided, they just replaced the prior version with this much better looking solution. I recall the old version was much more expensive. Again, I don't know how good this thing works.