RTKDCMB and MJS seem to have laid it all out for you. For safety, you should be doing a degree of conditioning in any event, for when you have no option but to check/block, for when you get caught and for when your own attack is stopped cold with an effective block.
Then there is evasion or tying the guy up or smothering/jamming the kicks by being in close.
I have a TKD and then Goju Ryu karate background so I am not a guy who naturally fights by way of leg attrition but have entered a few open tournaments, Kyokoshin and kickboxing tournaments and I don’t like playing that attrition/weathering game. Most of my fights against kickboxers have been, as MJS says, with the use of timing and distance. You need to read the low kicks coming but if you are in the right mindset a lot of these can be avoided. Obviously you need to work on your timing, and, despite what some say, in my view this is best done with sparring and obviously with various opponents (there are also specific exercises/drills you can do with your coach or friends to enhance this). Once you get your timing, speed and reflexes honed you can then also play an effective (but potentailly dangerous) game of baiting, which I have used in tournaments to (sometimes) good effect, where many expect you to weather or check as the norm. You can leave your front leg out there a bit as a target and then pull it back and counter with the same leg with a high kick (or from what was the back leg with a front kick), your counter can also be against the support leg or the opponent’s striking leg as weight is put on it again as it touches the mat. Again, you need to be sure of yourself doing this (and have an idea of the guy you are up against) as it can otherwise go horribly wrong : )
Another counter, which is very hard to pull off (at least for me) and one I spent many months working on (for some reason I just love the idea of the move) (and still seldom used or felt comfortable using – but it does have its place!) was to attack the support leg of your opponent as he executes a leg attack off the back leg. As he starts to execute his attack you (very) quickly attack his front support leg (either by leg/knee (if permitted) attack or sweep) with your own front leg. You need to be good at reading the roundhouse leg attack coming and need to react - almost pre-empt it very quickly. This is a nasty counter and almost always (actually, I would say 100%) results in the opponent going down if successful. If you leave it too late when moving in you can obvuiously get hurt badly. But if you do muck it up you are often in close enough to smother or inadvertantly negate the round house leg attack in any event as your body is positoned much closer into him and the leg target is no longer presented. However, it is not something you want to get wrong so it’s not something I have used much or see being used (but I have a soft spot for it as when done properly it is a beauty). I trained a lot with team mates on this move and also (mad as it sounds) by using a tree limb or the like and placing this at an angle against another fixed post or tree and practicing explosively moving in and attacking with the front leg. Those are some secret training tips I’ll let you have for free.
Another word from experience, if you are entering these kickboxing tournaments and if you are fighting it in your style (an evasive style), if you are unable to win by KO you really need to compensate by landing strikes and being seen to land strikes and to dominate in that manner. I have found that if you end on what would be otherwise a draw or where no fighter has really bettered or damaged the other, the evasive style and lack of “committal” may be misread in this environment and go against you on the score card.
