Bathtubs for veges

I've been thinking about growing our veges in bath tubs. We want to expand the amount of our own food that we grow. We can't use timber bordered beds because of the termites that naturally reside round the place. I won't use treated pine. I thought about a few other things but they were all ruled out for one reason or another.

We do have one colourbond bed but it's just not viable financially to deck out our entire yard with these, as lovely as they may look. Funnily enough before they came popular I was hunting round for old water tanks to grow veges in lol and now 'colourbond' planters are all the rage!

So we'll get old bath tubs, raise them up on a couple of courses of bricks with mesh between the bricks and base of the bath (to stop rust if they're that kind?), then 'wrap' them in discarded/reclaimed corrugate to pretty them up, eventually at least, and as we gather the colourbond. It was initially an idea to make our own colourbond planters but it would mean corners (because we don't have a corrugate bender) and then enough to support them. So this way with the baths as the planters, the corrugate is the 'finish' and not the 'structure', so it won't need reinforcing because it won't be containing a load.

Benefits of bath tub planters:

• raised off the ground - better height for working and picking
  
• not planting into existing soil - no grass or very minimal grass can get in. More idea over exactly what soil is going in there.
• less soil needed. Our big colourbond planter we filled the bottom with 'sand' and then put the manures and good stuff on top of that. So 'waste' at the bottom - and certainly if you filled the whole lot with compost/manure etc esp if you had to buy it, it would be more resources in the set up. With the bath tubs, pretty much it's only the soil you'll use, that will go in.
• Can get them secondhand/reclaim for free or for small cost. The more battered the cheaper they'll be. bonus :)
  

I've been Googling round the place and have asked on a couple of forums and found a small amount of info and ideas (like this hydroponics setup) but if anyone can help please point me in the right direction!

Questions:

• Anyway, my q was, what baths aren't ok?
• how long would enamel ones last (if they're ok to use) before they rust through?
  

Enamel ones I thought would be no good because they would rust, but then someone else said the ... [newer ones, are they acrylic?] would not be ok either because of what they're made of and leaching issues. I don't know a whole lot about it and was hoping someone on here would and be happy to share please.

UPDATES

• some info on Nickel leaching here and on the poster's remedy which was pond liners... it's a thought for sure. Pond liners ok with edibles though?