Generally speaking, A 1000 watts RMS amplifier is a little too much for two 300watt RMS subs. I think I know why you have gone through so many subs.
But that's where brand name and model quality will make up the difference.
Overpowering is fine, but when you start talking almost double the recommended power, then problems are likely to occur. If you match RMS ranges you may not have the upper most SPL possible, but you'll have a system that lasts longer than 1 year.
I wouldn't give a 300 watt sub more than 450 watts or so (maybe 500 if it's a premium brand). I personally send about 950 watts to a 750 watts sub (~26% overpowered). With this setup I know I'm trading a little SPL for a little longevity.
Same for underpowering, but the reason why is different. In a nutshell, underpowering is bad for a system when the user cranks up the volume too high to compensate. Signal processors start can't compete or are over driven into signal clipping, and distortion, both of which are not good for drivers (speakers).
I say this because I don't like buying systems every few months. Research and plan, and get a balanced system and it will last you for years. Just remember that you have to double
power output to gain an extra 3 dB. So Putting 500 watts into a 300 watt RMS subwoofer may only result in 2 extra dB, and it may die in 6 months versus 18 months. (Generally speaking)
RMS is the level of power the product is rated to withstand continuously without any damage what-so-ever.