I'm suprised no-one has answered this by now.

I have no ideas, personally. I'd be tempted to scour the area and ask for cuttings from someone who has one that takes your fancy.

The trouble is that they are grafted into vigorous rootstocks.

Well, don't try Compassion. Apart from the soppy name, it grows all angular and elbowy and won't lean itself languorously against the house wall in the required way. But it's a climber, not a rambler. Zephirine Drouhin, though beautifully named, is a weedy thing that just can't be bothered to grow properly. Dorothy Perkins and American Beauty (homage to the late, great Gerry Garcia??) are wilful and disobedient growers and will have your eyes out at pruning time. Summer Wine is gorgeous by name and appearance but really wants to be a bush. Rambling Rector is probably not suitable unless you live in a castle and your name happens to be Sleeping Beauty. There, that's the sum total of my rose knowledge.
I'd stick to pyracantha, really, much simpler!

I suggest you plant in a bottomless tub of good compost. This will allow the rose to get the benefit of the good soil, but it can put its roots down. Whatever you plant you will have to water regularly. Bear in mind that true ramblers only flower once. Those I have experience of, and which are tough, are Paul's scarlet - bunches of small red flowers, Frances E. Lester - large bunches of pinkish white single flowers resembling a dog rose, but many more flowers, and American Pillar - bunches of bright pink single flowers, tough as old boots. Albertine is also very lovely and a wonderful scent - copper pink semi double.(my favourite) One which I have also found successful and tough, but which is not a true rambler, but you get some flowers after the main flush, is Maigold - orange flushed yellow semi double, tough but thorny. Lastly, I have not tried it myself, but the yellow Banksian rose is slightly tender and would like a south wall. It has small double yellow flowers. My advice is to plant in autumn or winter so the roots get time to settle in before the stems start growing.

Peter Beales website is a good resource to research rose varieties. Choose "Climbers, Ramblers and Scramblers" from the "Choose a Family" option on the left-hand side and have a browse. The further details option for each rose shows varieties which are tolerant of poorer soils.

Here is a link that might be useful: Peter Beales Roses

Thank you to everyone who replied, you've been most helpful - and the Peter Beales site has me wanting at least ten of each!

you need to remember that ramblers usually flower once a year either early, mid or late and do need room to grow e.g. Kiftsgate can reach 30 feet. You also need to look for plants which either repeat or are continuous flowerers. Maigold is a stunner but flowers once. From experience I would reccomend Handel, Compassion, Dublin Bay and Galway Bay. You will also find that many are tolerant of poor soils, north walls and pot culture. Email me and I'll send you a climbing rose comparison chart I made.

A rose question before I mention my favorites,all from Peter Beales over the last ten years.
I have some roses from cuttings,doing well and flowering. Will they be as hardy as roses that have been grafted?
I have 3 white ramblers all 30 ft. Rambling rector,seagull and Kiftsgate. I battle with them every autumn.
My favorite climbers are Albertine and Madame Alfred carriere.but then they are the only ones I have that have a typical round the door English rose look.
The rest are all chosen to look a bit wild such as
Meg merrilees ,Alba semi plena,Moyesii nevada , moyesii geranium and rubrifolia etc.
I have no idea how any of them are suited to poor soil however.

?

Have a look on Google's image search at some pictures of Blush Rambler and see what you think. If you feel that that might be a bit too strong-growing on a porch, there's a more unusual rose called Spectabilis that is much more restrained in its growth. The best advice that anyone can give you about this is that you choose a rose that is known to keep its health.