Structual help needed lpg tank cracking mounts

[TurboRA28]

Hi all, i've had a problem lately with the 80 series which is on LPG. It's been on gas for around 9 years now and around 6 months ago the bracing under the rear floor that the gas tank bolts to cracked. I welded it all up but now 6 months later it has cracked again. So I figure I need more than just welding up but some additional strength.
Just wanted some advice on how to strengthen the area..

Its like this
---------------- <-cross bar between chassis rails
x x <-x indicates where the cracks are occuring
| |
| | <-this is what the tank brackets bolt to. Basically just 30mm RHS.
| |
x x
----------------

So what is my best way to strengthen this up..??
Thanks
Joel
So

[allencr]

---------------- <-cross bar between chassis rails
x x <-x indicates where the cracks are occuring
| |
| | <-this is what the tank brackets bolt to. Basically just 30mm RHS.
| |
x x
----------------

I don't know what that describes, but doublers & gussets.

[cambelt]

30 MM RHS is far too small for cross bars , Make some new ones up out of 50X50x6 Angle or bigger /thicker section RHS .
Sepending on what tank you have you can just buy a new cradle to suit your car .
Dave