A modular endovascular graft assembly comprising: a main elongate tubular graft body (10, 12) having a proximal open end and an opposed distal open end, defining a graft body wall having a proximal portion, a medial portion, a distal portion and an open lumen therein between; the graft body wall comprising a proximal neck portion disposed at the proximal end; the graft body wall comprising at least one circumferential inflatable channel disposed towards the proximal portion of the graft body wall near the proximal open end of the main tubular graft body (10, 12) and distally prior the proximal neck portion; the graft body wall comprising a plurality of circumferential inflatable channels disposed towards the distal portion of the graft body wall near the distal open end of the main tubular graft body (10, 12); a proximal expansion anchor disposed at or secured to the proximal neck portion of the graft body wall; a first and second elongate tubular stent-graft extensions (118, 120, 300) percutaneously disposed into the distal end of the tubular graft body (10, 12), the first and second stent-graft extensions (118, 120, 300) having respective proximal open ends and opposed distal open ends, defining graft body walls having a proximal portions, medial portions, distal portions and open lumens (119, 121, 320) therein between; characterised in that the first and second elongate tubular stent-graft extensions (118, 120) comprise a tubular stent securably disposed between a graft liner and a graft cover, the stent comprising an undulating wire having opposed first and second ends and being helically wound into a plurality of approximate circumferential windings to define a stent wall, the undulating wire having a plurality undulations defined by peaks and valleys with peaks of adjacent approximate circumferential windings being separated by a distance, and peaks of one circumferential winding being substantially aligned with peaks of an adjacent winding; and in combination, the proximal portions of the first and second stent-graft extensions (118, 120, 300) are conformable to a shape of the open lumen of the main graft body (10, 12) and are configured to prevent flow of bodily fluid between outer proximal portions of the first and second stent-graft extensions (118, 120) and the open lumen of the main tubular graft (10, 12). a main elongate tubular graft body (10, 12) having a proximal open end and an opposed distal open end, defining a graft body wall having a proximal portion, a medial portion, a distal portion and an open lumen therein between; the graft body wall comprising a proximal neck portion disposed at the proximal end; the graft body wall comprising at least one circumferential inflatable channel disposed towards the proximal portion of the graft body wall near the proximal open end of the main tubular graft body (10, 12) and distally prior the proximal neck portion; the graft body wall comprising a plurality of circumferential inflatable channels disposed towards the distal portion of the graft body wall near the distal open end of the main tubular graft body (10, 12); a proximal expansion anchor disposed at or secured to the proximal neck portion of the graft body wall; a first and second elongate tubular stent-graft extensions (118, 120, 300) percutaneously disposed into the distal end of the tubular graft body (10, 12), the first and second stent-graft extensions (118, 120, 300) having respective proximal open ends and opposed distal open ends, defining graft body walls having a proximal portions, medial portions, distal portions and open lumens (119, 121, 320) therein between; characterised in that the first and second elongate tubular stent-graft extensions (118, 120) comprise a tubular stent securably disposed between a graft liner and a graft cover, the stent comprising an undulating wire having opposed first and second ends and being helically wound into a plurality of approximate circumferential windings to define a stent wall, the undulating wire having a plurality undulations defined by peaks and valleys with peaks of adjacent approximate circumferential windings being separated by a distance, and peaks of one circumferential winding being substantially aligned with peaks of an adjacent winding; and in combination, the proximal portions of the first and second stent-graft extensions (118, 120, 300) are conformable to a shape of the open lumen of the main graft body (10, 12) and are configured to prevent flow of bodily fluid between outer proximal portions of the first and second stent-graft extensions (118, 120) and the open lumen of the main tubular graft (10, 12).