Where to fit back box. on rails or off.

I've got myself a back box (Ultra 500) now and my husband says it's better to take the bottom bike rails off and I say NO. He seems to think it would be stronger. Anyone help me?????  
To sit on rails or not   

Hi Rose , our previous 2 coachbuilts had the Fiamma back box sitting on the rails. It fitted perfectly and the rails support the bottom of the box uniformly along its length adding extra security.  2 of the u brackets came square shaped to fit over the rails. I did fit 2 extra brackets at the top rear to support the box around the hinge area but probably me being a bit belt and braces!  Feel free to totally disregard anything I say as I am not a structural design engineer!

Hi Rose

Yes - what Kaspian said. The additional support of the rails is worth considering.

I'm not a structural engineer either , but like Kaspian I can apply a bit of logic - and what he says about the additional support makes perfect sense to me.

Tell Himself we'll be round to duff him up if he gives you aggro . . . unless he's generous with the beer of course! 

He he I'll tell him that but you'd probably knock him for six as he's decided he's become an old man. It's only a second hand box and will have to get some more u bolts but holes line up well and only eight have been drilled. 
And I will have my way now as you have said "leave the rails  on"  

I have the same box and wouldn't wish to risk using it without the bottom rails to take the weight, particularly since we sometimes transport our generator inside the box.  

Not sure how your husband's logic works if he believes it would be stronger without?*

We also have the bottom support extended so we have four bike rails fitted and with the box in place we can still carry one bike behind it (not with the generator in that case though so as not to exceed the weight limit!)



cheers
Roger

* PS I was originally thinking he meant to take the whole bottom assembly off but just realised he probably means removing the bike rails but not the bottom support.  That might work but I would still say leave the rails on though as that helps distribute the load. All the official Fiamma pictures and instructions I've seen show the rails in place.