Don't - I used to work check in at both Terminals 3 and 4 - it is frightening how much cr*p people take. I can understand if you have kids/babies - but otherwise ......
Certain flights have a trend for those checked large washing bags tied with string, various rickety cardboard boxes tied with string and packing tape, with oily stains on.
I can go away for 2 weeks on a beach with hand luggage only, though it has got more difficult as airlines have restricted the weights there as well.
I am lucky enough to board at the first station on the line in Zone 6, and probably the last one you are guaranteed to get a seat, unless there are delays. 99% of the time I sit in the same seat, next to the same person, right near the doors with my Brompton sitting close beside me with my left hand on the saddle in case it tips over when the train decides to get a shift on and start swaying about a bit.
I did buy the cover with the bus in mind though - the train station from which I get 2 trains home, is right next door to the bus station from which the previously mentioned 285 bus starts its journey, and in the bad weather before Christmas (2010 BB (Before Brompton)), the trains were totally messed up, but the buses were running. On the rare (as yet unused occasion) that I might have to resort to the bus for the whole journey, it's peace of mind.
Mind you, the total loss of the trains has happened - but it was just after the clocks changed, when we started getting the nice weather, so I cycled through the park and then all the way home in the end - but I wouldn't want to do it in winter (the park would be closed for starters).