What's the easiest and cheapest way to put down flooring in a trailer?

Floating laminate floors are probably the easiest with a large price range. Lots of different wood colors also. Use quarter round edging after you are finished along the walls. Measure length X width to get the area you need to cover.

The only caution I would say is that trailers have little insulation in the floor and laminate floors will not add much more. Also, if she is elderly, they can be slippery.

If your able to take up the floor per-room and use that as a template. Shop ollies, carpet store have pieces left over from big jobs at low costs for small rooms and you can make the cut from the template. Also check Craigslist for carpet installers.

I would go to youtube. There are videos on almost every issue. Also, Lowe's offers workshops.

first decide what material you would like to use to replace the carpet....laminate, vinyl, hardwood, ceramic. Each product will require slightly different prep and application. Check with the building supply store when you buy the product for the best method. Tear out the carpet, remove any tacks/staples etc from the floor. Repair any problems with the sub floor, then install as suggested.

Are you looking at possibly tile or laminate? The best way to proceed would be to remove the old carpet, padding, tack strips and make sure the subflooring is smooth, clean and fairly level. If there is deep variations in the level of the floor new subflooring may be needed. If you are doing laminate flooring that will be fairly simple. Just roll out your underlayment and stagger the boards as explained in the directions. Check out YouTube for how-to's, that site is a wealth of information