Hi tbcgaz,
I am a 38 year old male Type 1 who has been following a low carb, less than 30g per day, diet for several months now. I do not play Rugby but I do weight train and cycle quite a bit. I do not take any extra carbs pre or post training and generally I find that my levels stay within a fairly tight range and tend not to dip all that much. For example, I cycled home from work on Monday evening - which is about a 10 mile commute and quite hilly - my BG was 6.1 before I set off - tested about 20 mins post cycle and it was down only a fraction to 5.6.
I find that when I follow the low carb diet exercise has far less of an impact than when I used to carb load - this could be down to the fact that there is less circulating insulin but I suspect also because your body has much easier access to fatty acids that you burn instead of the carbs when low carbing - overall I feel much better working out this way than I ever did whilst eating the carbs.
Like everything experiment and keep testing you will soon get the hang of it....as for muscle building you will find that you have no problems with that either - you will lose fat whilst maintaining or building muscle..try it...just keep an eye out for your BG numbers increasing if you lift heavy - you may need a little fast acting insulin to balance this out - something to do with stress hormones being released that increases your blood sugar I believe.
You may also want to read Fergus's posts on low carb and exercising as he is far better at explaining all of this than I am - Fergus keeps fantastic control and is a keen cyclists/runner so he has a vast amount of knowledge on the subject.
All the best, Fletch.