Yip I was the same I partially replaced the carpet in the van with lino at the entrance and the end WC washroom. I bought a cut off from a carpet store was about £20. A quick tip save your old carpet and use as a template for the new one.
Depending on your DIY.for our old caravan I went to a carpet wearhouse and bought a 19 roll end for £20.laid it out outside on the drive.cut out the old one and used this as a template,cutting half inch oversize all the way round.lifted it in and cut to fit.still looked good when we sold it.plus the added bonus they have carpet fitters if you need one.do not put two carpets down as your cupboard and bathroom door may not open.you can buy as we did for the new van a carpet runner,these are about three foot wide.i priced one up a few months ago and the cost was £40 for 19 foot.
------------- the only silly question is the one you do not ask.