My daughter uses Advent bottles and we find if we remove the inner liner we can fit the 260ml Advent bottles and lid in the sterilizer when using it for cold water sterilization.
We have done this at the side of the road. Have the water including the disolved sterilizing tablet in a bottle. Put the baby bottle base first into the sterilizer (leave inner part out) add other parts of the bottle including the lid and pour in the sterilizing water so it fills the bottle and covers everything. You can then screw on the top.
After the required minutes open the little hole in the lid and pour out the water into a plastic jug or as we do we use a funnel to put it back in the bottle. You can use the same sterilizing water again for a few times during 24 hrs.
We then take out the bottle etc and fill the bottle with milk from a carton. We pour some hot water from a vacuum flask into the sterilizer and stand the bottle of baby milk in it. You just have to make sure that children don't think the bottle of "sterilizing water" is lemonade.
If you are at home and want to use it in your microwave, a 260ml Advent bottle will fit inside the inner part except for the lid. Stick the lid in first and sterilize it - take it out and put it somewhere safe. Put the bottle and other parts in the holder and sterilize them.