The underslung spare wheel carrier should be easy to fit but you need to make sure it will accommodate the wheel size that you have as I think some are deeper than others especially as some are designed to carry a steel rim wheel and others an alloy wheel. The link below may help in maintenance and assembly of the carrier.
Make sure you can get the spare wheel out if you have a puncture as the Alko carriers need good ground clearance and enough room to pull out the wheel (could mean you could not park close to side of road).
------------- 'A sure cure for sea-sickness is to sit under a tree'
read on here they can after a few years of use be a pig to remove if you have a punture,so needs to be greased or oiled each year.you dont want to find out at the side of the road.
------------- the only silly question is the one you do not ask.
Michael's right, they do need some annual TLC to make sure they're free to retract easily. They are telescopic and get an absolute b****r to shift if left.
I clean mine up and apply some Coppersil to the tubes; the thing always moves with no difficulty.
Incidentally, hopes yours fit's ok. They are easy enough to install but they are available in different overall lengths, depending on chassis dimensions.