I have only been using Roll20 for a few weeks, so you certainly have more experience with the tool than I do. I have just been looking at ways to use the features of the tool to allow HARP to be played. As I learn more about it, I get new ideas. I also think that the free subscription I am using currently, may not be the answer as the free level does not have all the features enabled.
So, I’m wondering how you’re making roll20 work for your HARP game? It seems that you’d have to make lots and lots of macro’s without a working roll20 character sheet. Do you just have a macro for the open ended d100 and then refer to sheets outside of roll20 for results?
I use the default character sheet of None. This gives me a character sheet with attributes and abilities. I populate the attributes with the characters skill such as 'Perception' and set the value of the attribute to the skill modifier for the character. In the abilities side, I then add an ability that references the attribute, makes an exploding roll adding the modifier from the referenced attribute value. We only use this method for skill checks. Combat and the maneuver table still needs to be done with a paper lookup once the value is figured out.
At first we were only using the mapping and tokens to make sure everyone had a good idea of what the tactical situation was. I came up with the idea to use it because one of my group is not able to be at the table for a while. It worked great just using the chat window roller ( /r d100!>95) to make his rolls and then do the lookup in the critical/maneuver charts. I thought the tool was awesome after using it and I have moved all my map and character location presentations to the tool.
I think for me, one advantage that I have is that I am a programmer. I know some very effective short cuts (writing code to write other code) to make repetitive tasks go quickly so most of the macro writing is automated outside of the roll20 app and copy pasted into the fields on the ability editor.
I migrated my group from D&D 5e about a year ago. The main reason being, the players were wanting more flexibility with character development. I found HARP and thought that it would be a good alternative that would not be too difficult to learn. I have now run about 50 sessions of HARP and have heard no complaints.